Power steering gears are common in modern vehicles. Typically, one or more rigid shafts connect a vehicle steering wheel to an input shaft of the power steering gear. The rigid shafts must be routed from the vehicle steering wheel to the input shaft of the power steering gear. Routing the rigid shafts between the steering wheel and the steering gear is often difficult, as other vehicle components must not interfere with the shafts.
Some known vehicle steering systems have eliminated the rigid shafts. Such systems are commonly referred to as “steer-by-wire” systems. In some steer-by-wire systems, there is no mechanical connection between the steering wheel and the steering gear. An electronic system is provided that is responsive to operator-applied inputs to the steering wheel for controlling actuation of the steering gear. With no mechanical connection between the steering wheel and the steering gear, steering control of the vehicle is lost if the steer-by-wire system fails.
Other known vehicle steering systems enable multi-axle steering. A multi-axle steering system generally includes a front steering gear for turning front steerable wheels and a rear steering gear for turning rear steerable wheels. The rear steering gear is responsive to vehicle speed and to the steering angle of the front steerable wheels. When the vehicle speed is below a predetermined level and the steering angle of the front steerable wheels is greater than a predetermined amount, the rear steering gear is actuated for turning the rear steerable wheels. As a result, the rear steering gear turns the rear steerable wheels to supplement the steering provided by the front steering gear.
Caster causes a road wheel to align itself with the direction of vehicle travel. Caster provides returnability in conventional steering systems. Auxiliary axles of multi-axle vehicles commonly use caster to steer the wheels. Such “self steered” axles cannot generate a side force to help turn the vehicle.